This invention relates to a magnet apparatus used chiefly for an ion source for manufacturing of a semiconductor.
It has been proposed in recent years that a precision processing operation for manufacturing a semiconductor can be carried out by a reactive ion beam etching in order that a more precise product may be obtained with better control and less contamination. An ion source used for this precision operation is usually constructed, as show in FIG. 1. A vacuum electric discharging chamber a is charged with a reactive gas such as CF.sub.4, C.sub.3 F.sub.8, C.sub.4 F.sub.8 or the like. The chamber is provided at its outer periphery with plural electromagnets b, b, so that ions thereof generated in the electric discharging chamber a by introduction of microwave thereinto are inducted, by means of an induction electrode c, towards a workpiece e provided in an adjacent treatment chamber d for etching the same.
It is necessary, in this case, that, in order to form an electron cyclotron resonance magnetic field in the electric discharge chamber, the plural electromagnets b, b, are controlled to produce a magnetic field having a gradient with an intensity larger on the microwave inlet opening side of the chamber a and smaller on the ion outlet opening side thereof as shown in FIG. 2. However, this arrangement is defective in that it is not always easy to control the electric current to each of the plural electromagnets b, b. A comparatively large capacity electric power source is required for achieving this control. Additionally, water-cooling thereof is required.